As consumer drones have become more commonplace, so too have concerns that owners might be tempted to use them for snooping. Researchers have now developed a way to uncover such activity, coming up with a way to intercept a drone's radio signals and tell whether it's been filming things that it shouldn't.

The technique was developed at Israel's Ben-Gurion University of the Negev, and it centers on the first-person view (FPV) radio signals being transmitted from an airborne drone back to its controller. Knowing that these signals, which the drone uses to relay its video stream, will change in response to visual stimuli, the team set up traps to catch out snooping drones.

In one experiment, the team acted out a scenario where a DJI Mavic drone was used to film a neighbor's house. A type of smart film was placed on the surface of the windows, which allowed the windows to be switched between opaque and transparent. This flickering caused changes in the bitrate of the drone's radio signals, which could then be picked up by the team's proof-of-concept system.

"The beauty of this research is that someone using only a laptop and an object that flickers can detect if someone is using a drone to spy on them," says Ben Nassi, a Ph.D. student of Prof. Yuval Elovici's in BGU's Department of Software and Information Systems Engineering. "While it has been possible to detect a drone, now someone can also tell if it is recording a video of your location or something else."

In another demonstration, the team used an LED strip on a person wearing a white shirt to create a similar effect, picking up uncharacteristic spikes in the intercepted radio signals to prove that the drone was filming that particular subject. The team says the technique doesn't require any advanced hacking skills and could be used on any laptop running Linux OS.

"This research shatters the commonly held belief that using encryption to secure the FPV channel prevents someone from knowing they are being tracked," Nassi says. "The secret behind our method is to force controlled physical changes to the captured target that influence the bitrate (data) transmitted on the FPV channel. Our findings may help thwart privacy invasion attacks that are becoming more common with increasing drone use. This could have significant impact for the military and for consumers because a victim can now legally prove that a neighbor was invading their privacy."

A paper detailing the technique is available online, while the video below shows it in action.